The prior art contains many electrical stimulation devices based on the use of pulse generators for transcutaneous application of electrical pulses to the nerves and muscles. Examples of these are listed below:
U.S. Pat. No. 4,699,143 to Dieken et al; PA1 U.S. Pat. No. 4,230,121 to Stanton; PA1 U.S. Pat. No. 4,201,151 to Keller; PA1 U.S. Pat. No. 4,173,741 to Kameny; PA1 U.S. Pat. No. 4,144,893 to Hickey; PA1 U.S. Pat. No. 4,121,594 to Arp et al; PA1 U.S. Pat. No. 4,062,365 to Kameny; PA1 U.S. Pat. No. 4,765,322 to Charmillot et al; PA1 U.S. Pat. No. 4,763,656 to Nauman; and PA1 U.S. Pat. No. 4,408,608 to Daly et al. PA1 first pulse generation means for providing a first variable frequency and pulse width output; PA1 second pulse generation means for providing a second variable frequency and pulse width output; PA1 switching means for providing a series of pulse trains as a combination of said first and second pulse width outputs on at least one output channel; PA1 means for modulating said series of pulse trains so as to provide a pulse waveform envelope having an increasing amplitude during a predetermined interval; and PA1 current amplification means for providing said modulated series of pulse trains to at least one pair of electrodes with substantially constant current in relation to tissue impedance for increased penetration, said amplified modulated series of pulse trains providing electrical stimulation of the large myelinated nerves with significantly increased energy at relatively low skin irritation and pain levels.
In addition to the above listed patents, my previous U.S. Pat. No. 4,233,986 disclosed apparatus and methods for controlling pain by transcutaneous electrical stimulation, based on use of a pulse generator with various modulation techniques including frequency and pulse width modulation.
In U.S. Pat. No. 3,983,881 to Wickham, the energy content of each pulse train is modulated by increase and decrease of the pulse width, for gradual contraction and relaxation of the muscles. U.S. Pat. No. 4,759,368 to Spanton et al discloses independence between variation of the pulse rate and modulation of the pulse amplitude and width, to avoid the phenomenon of accomodation in nerve stimulation.
U.S. Pat. No. 4,431,000 to Butler et al discloses application of an irregular pulse train by use of a pseudorandom pulse generator, with the average pulse rate on the order of the alpha rate, and is adapted to allow the nerves to repolarize while reducing the effect of variables such as skin resistance. The base pulse rate, pulse width and amplitude are also adjustable.
A study of the wide range of neuro-stimulators reveals that most of these instruments use a pulse transformation technique, with low voltage provided by a battery source. In order to reduce the size of the instrument by reducing the pulse transformer dimension, a miniature high frequency ferrite core is used, but this limits the application of pulse shaping and stabilization techniques. The early transcutaneous nerve stimulators (TNS) operated within the 40-300 microseconds pulse width range, with a frequency range of 1-150 pulse/second. The problem with these instruments is that they do not account for basic neurophysiological behavior, and exhibit low efficacy, causing pain and irritation of the skin, since they operate on the skin surface area where the pain receptors are concentrated.
It is known from the behavior of the nervous system that electrical stimulation of the large myelinated nerves is more effective in reducing pain, since this provides access to a higher level of the nervous system via the synapses, closer to the spinal cord and the brain.
It is therefore an object of the present invention to provide a neuro-stimulator device which reduces pain, while achieving higher penetration of the biologicial tissue to reach the large nerves at a higher energy level without causing skin irritation.
It is a further object of the invention to achieve better coordination between the electrical pulses and the physioligical behavior of the nervous system, by accounting for the reaction of nervous system to the applied pulse waveforms.
Similarly, it is an object of the invention to achieve better coordination between the electrical pulses and the physiological behavior of the muscular system.
It is still a further object of the invention to avoid the phenomenon of accomodation so that the nerves and/or muscles remain responsive to the applied electrical stimulation.
It is yet another object of the invention to achieve electrical stimulation at a constant current via compensation for the changes in the tissue impedance.